The invention concerns a method, and a device for carrying out the method, for purifying oil-containing and watercontaining roll scale sludge with which the roll scale sludge is introduced to a heatable treatment region in a first drying step.
A method and a device of the above mentioned kind are known in the art from the brochure "Thermocon-Thermische Reinigung von kontaminierten Schuttgutern" [Thermocon, Thermal Purification of Contaminated Bulk Products]published by Lobbe Umwelttechnik GmbH & Co, D-58642 Iserlohn, 6/1996.
In steel-processing industry, initial raw steel product is processed into an intermediate or end product via shaping processes (rolling, forging, etc.). During processing, in addition to the intermediate or end product, waste products in the form of iron-containing particles (iron powder, iron chips and the like) also occur. Due to the action of oxidizing gases on these waste products, an iron oxide, which is called roll scale, is rapidly produced. A recycling method has the goal of returning this roll scale into a usable initial product. This is, however, made difficult by the fact that the roll scale is contaminated, via lost lubricant or leakage from the processing installation, with oils, fats and other liquids. As a result, this soiled roll scale, designated as roll scale sludge, is no longer suitable as a raw material for recycling into the production of steel. The roll scale sludge can then only be integrated into the raw material cycle for steel production if the oil and water can be removed. The need to purify oil- and water-containing roll scale sludge is obvious in view of the fact that, alone in the Federal Republic of Germany, approximately one million tons of contaminated high quality roll scale is produced per year in the steel processing industry. For environmental reasons it is therefore important to separate water and oil from the roll scale in order to be able to reuse the extracted iron oxide in high-temperature furnaces for the production of steel.
The above mentioned Lobbe brochure has already proposed a method with which the roll scale sludge is heated in a bulk product container. The bulk product container comprises a reactor in which the roll scale sludge is heated from below so that the contained water initially evaporates and rises. The organic contaminants (oils, fats) are thereby also intended to be driven out of the roll scale sludge. The resulting exhaust vapors can be removed and purified from the upper region of the bulk product container. This type of treatment of soiled sludge is primarily suitable for sludges having a high percentage of water. If, however, the fractions of oil and fat in the contaminated sludge increase, the purification loses its effectivity or the processing time of the sludge continuously increases. In particular, the desired treatment of large quantities of oil- and water-containing roll scale sludge in as short a processing time as possible is not feasible.
The conventional process works on a pure thermal basis. DE 29 18 820 C2 therefore additionally proposes the admixture of chemical reactants during the cleaning of the bulk and/or flowing materials in order that the reactants act on the bulk material. This type of utilization of additional reacting products requires additional processing steps and is associated with additional recycling problems such as disposal of the reaction products. Downstream filters, washers or condensers are required for recapturing the reactants.
Although it is desirable to be able to purify the oil- and water-containing roll scale sludge based on thermal processes alone, the conventional useful large scale commercial industrial methods incorporate auxiliary materials (hydrophobyrized calcium, steam as stripping agent and the like) to separate the oil. The waste products which thereby result must likewise be disposed of and are difficult to recycle.
It is therefore the purpose of the present invention to improve purification of oil- and water-containing roll scale sludge without additional auxiliary materials utilizing only thermal energy and in a more effective fashion suitable for large-scale commercial applications.